In the production process of semiconductor integrated circuit devices, after a great number of integrated circuits are formed on a wafer, a probe test for sorting defective integrated circuits is generally conducted by inspecting basic electrical properties of each of these integrated circuits. This wafer is then cut, thereby forming semiconductor chips. Such a semiconductor chip is contained and sealed in a proper package. Each of the packaged semiconductor integrated circuit devices is further subjected to a burn-in test that electrical properties thereof are inspected under a high-temperature environment, thereby sorting latently defective semiconductor integrated circuit devices.
In such electrical inspection of integrated circuits, such as probe test or burn-in test, a probe member is used for electrically connecting each of electrodes to be inspected in a wafer or integrated circuit device as an object of the inspection to a tester. As such a probe member, is known a member composed of a circuit board for inspection, on which inspection electrodes have been formed in accordance with a pattern corresponding to a pattern of electrodes to be inspected, and an anisotropically conductive elastomer sheet arranged on this circuit board for inspection.
As such anisotropically conductive elastomer sheets, there have heretofore been known those of various structures. For example, Japanese Patent Application Laid-Open No. 93393/1976 discloses an anisotropically conductive elastomer sheet (hereinafter referred to as “dispersion type anisotropically conductive elastomer sheet”) obtained by uniformly dispersing metal particles in an elastomer, and Japanese Patent Application Laid-Open No. 147772/1978 discloses an anisotropically conductive elastomer sheet (hereinafter referred to as “uneven distribution type anisotropically conductive elastomer sheet”) obtained by unevenly distributing particles of a conductive magnetic substance in an elastomer to form a great number of conductive parts extending in a thickness-wise direction thereof and insulating parts for mutually insulating them. Further, Japanese Patent Application Laid-Open No. 250906/1986 discloses an uneven distribution type anisotropically conductive elastomer sheet with a difference in level defined between the surface of each conductive part and an insulating part.
In the uneven distribution type anisotropically conductive elastomer sheet, the conductive parts are formed in accordance with a pattern corresponding to a pattern of electrodes to be inspected of an integrated circuit to be inspected, and so it has advantages compared with the dispersion type anisotropically conductive elastomer sheet in that electrical connection between electrodes can be achieved with high reliability even to an integrated circuit small in the arrangement pitch of electrodes to be inspected, i.e., center distance between adjacent electrodes to be inspected.
In such an uneven distribution type anisotropically conductive elastomer sheet, it is necessary to hold and fix it in a particular positional relation to a circuit board for inspection and an object for inspection in an operation of achieving an electrical connection to them.
However, the anisotropically conductive elastomer sheet is flexible and easy to be deformed, and so it is low in handling property. In addition, with the miniaturization or high-density wiring of electric products in recent years, integrated circuit devices used therein tend to arrange electrodes at a high density as the number of electrodes increases and the arrangement pitch of the electrodes becomes smaller. Therefore, the positioning and the holding and fixing of the uneven distribution type anisotropically conductive elastomer sheet are going to be difficult upon its electrical connection to electrodes to be inspected of the object for inspection.
In the burn-in test, there is a problem that even when the necessary positioning, and holding and fixing of the uneven distribution type anisotropically conductive elastomer sheet to an integrated circuit device has been realized once, positional deviation between conductive parts of the uneven distribution type anisotropically conductive elastomer sheet and electrodes to be inspected of the integrated circuit device occurs when they are subjected to thermal hysteresis by temperature change, since coefficient of thermal expansion is greatly different between a material (for example, silicon) making up the integrated circuit device as the object for inspection and a material (for example, silicone rubber) making up the uneven distribution type anisotropically conductive elastomer sheet, so that the state of electrical connection is changed, and the stable connection state is not retained.
In order to solve such a problem, an anisotropically conductive connector composed of a metal-made frame plate having an opening and an anisotropically conductive elastomer sheet arranged in the opening of this frame plate and supported at its peripheral edge by an opening inner edge of the frame plate has been proposed (Japanese Patent Application Laid-Open No. 40224/1999).
This anisotropically conductive elastomer connector is generally produced in the following manner.
As illustrated in FIG. 20, a mold for molding an anisotropically conductive elastomer sheet composed of a top force 80 and a bottom force 85 making a pair therewith is provided, a frame plate 90 having an opening 91 is arranged in alignment in this mold, and a molding material in which conductive particles exhibiting magnetism are dispersed in a polymeric substance-forming material, which will become an elastic polymeric substance by a curing treatment, is fed into a region including the opening 91 of the frame plate 90 and an opening edge thereof to form a molding material layer 95. Here, the conductive particles P contained in the molding material layer 95 are in a state dispersed in the molding material layer 95.
Both top force 80 and bottom force 85 in the mold respectively have molding surfaces composed of a plurality of ferromagnetic substance layers 81 or 86 formed in accordance with a pattern corresponding to a pattern of conductive parts of an anisotropically conductive elastomer sheet to be molded and non-magnetic substance layers 82 or 87 formed at other portions than the portions at which the ferromagnetic substance layers 81 or 86 have been formed, and the corresponding ferromagnetic substance layers 81 and 86 are arranged in opposed relation to each other.
A pair of electromagnets, for example, are then arranged on the upper surface of the top force 80 and the lower surface of the bottom force 85, and the electromagnets are operated, thereby applying a magnetic field having higher intensity at portions between ferromagnetic substance layers 81 of the top force 80 and their corresponding ferromagnetic substance layers 86 of the bottom force 85, i.e., portions to become conductive parts, than the other portions, to the molding material layer 95 in the thickness-wise direction thereof. As a result, the conductive particles P dispersed in the molding material layer 95 are gathered at the portions where the magnetic field having the higher intensity is applied, i.e., the portions between ferromagnetic substance layers 81 of the top force 80 and their corresponding ferromagnetic substance layers 86 of the bottom force 85, and at the same time oriented so as to align in the thickness-wise direction of the molding material layer. In this state, the molding material layer 95 is subjected to a curing treatment, whereby an anisotropically conductive elastomer sheet comprising a plurality of conductive parts, in which the conductive particles P are contained in a state oriented so as to align in the thickness-wise direction, and insulating parts for mutually insulating these conductive parts is molded in a state that its peripheral edge has been supported by the opening edge of the frame plate, thereby producing an anisotropically conductive connector.
According to such an anisotropically conductive connector, it is hard to be deformed and easy to handle because the anisotropically conductive elastomer sheet is supported by the metal-made frame plate, and the positioning and the holding and fixing to an integrated circuit device can be easily conducted upon an operation of achieving an electrical connection to the integrated circuit device because a positioning mark (for example, a hole) is formed in the frame plate. In addition, a material low in coefficient of thermal expansion is used as a material for forming the frame plate, whereby the thermal expansion of the anisotropically conductive elastomer sheet is restrained by the frame plate, so that positional deviation between the conductive parts of the uneven distribution type anisotropically conductive elastomer sheet and electrodes to be inspected of the integrated circuit device is prevented even when they are subjected to thermal hysteresis by temperature change. As a result, a good electrically connected state can be stably retained.
By the way, in a probe test conducted to integrated circuits formed on a wafer, a method, in which a probe test is collectively performed on an integrated circuit group composed, for example, of 16 or 32 integrated circuits among a great number of integrated circuits formed on a wafer, and the probe test is successively performed on other integrated circuit groups, has heretofore been adopted.
In recent years, there has been a demand for collectively performing a probe test on, for example, 64 or 124, or all of integrated circuits among a great number of integrated circuits formed on a wafer for the purpose of improving inspection efficiency and reducing inspection cost.
In the burn-in test on the other hand, it takes a long time to individually conduct electrical inspection of a great number of integrated circuit devices because each integrated circuit device that is an object for inspection is minute, and its handling is inconvenient, whereby inspection cost becomes considerably high. From such reasons, there has been proposed a WLBI (Wafer Level Burn-in) test in which the burn-in test is collectively performed on a great number of integrated circuits formed on a wafer in the state of the wafer.
However, it has been found that when a wafer as an object for inspection is of large size of, for example, at least 8 inches in diameter, and the number of electrodes to be inspected formed thereon is, for example, at least 5,000, particularly at least 10,000, it is difficult to apply the above-described anisotropically conductive connector as a probe member for the probe test or WLBI test for the following reasons because a pitch between electrodes to be inspected in each integrated circuit is extremely small.
When a magnetic field is applied in the thickness-wise direction of the molding material layer 95 in the molding step of the anisotropically conductive elastomer sheet, conductive particles P present at a portion located inside among portions, which will become conductive parts in the molding material layer 95, for example, a portion (hereinafter referred to as “conductive part-forming portion X”) represented by a character X in FIG. 20, and surroundings thereof are gathered at the conductive part-forming portion X. However, not only conductive particles P present at a portion located most outside among the portions, which will become conductive parts, for example, a portion (hereinafter referred to as “conductive part-forming portion Y”) represented by a character Y in FIG. 20, and surroundings thereof, but also conductive particles P present above and below the frame plate 90 are gathered at the conductive part-forming portion Y. As a result, a conductive part formed at the conductive part-forming portion Y is in a state that the conductive particles P have been contained in excess, so that its insulating property with an adjacent conductive part or frame plate is not achieved, and so these conductive parts cannot be effectively used. In order to prevent the conductive particles P from being excessively contained in the conductive part formed at the conductive part-forming portion Y, it is also considered to reduce the content of the conductive particles in the molding material. However, the content of the conductive particles in any other conductive part, for example, the conductive part formed at the conductive part-forming portion X becomes too low, so that good conductivity cannot be achieved at such conductive parts.
In order to inspect a wafer having a diameter of, for example, 8 inches (about 20 cm), it is necessary to use an anisotropically conductive connector, whose anisotropically conductive elastomer sheet has a diameter of about 8 inches. However, such an anisotropically conductive elastomer sheet is large in the whole area but each conductive part is minute, and the area proportion of the surfaces of the conductive parts to the whole surface of the anisotropically conductive elastomer sheet is low. It is therefore extremely difficult to surely produce such an anisotropically conductive elastomer sheet. Accordingly, yield is extremely lowered in the production of the anisotropically conductive elastomer sheet. As a result, the production cost of the anisotropically conductive elastomer sheet is increased, and in turn, the inspection cost is increased.
The coefficient of linear thermal expansion of a material making up the wafer, for example, silicon is about 3.3×10−6/K. On the other hand, the coefficient of linear thermal expansion of a material making up the anisotropically conductive elastomer sheet, for example, silicone rubber is about 2.2×10−4/K. Accordingly, when a wafer and an anisotropically conductive elastomer sheet each having a diameter of 20 cm at 25° C. are heated from 20° C. to 120° C., a change of the diameter of the wafer is only 0.0066 cm in theory, but a change of the diameter of the anisotropically conductive elastomer sheet amounts to 0.44 cm.
When a great difference is created in the absolute quantity of thermal expansion in a plane direction as described above between the wafer and the anisotropically conductive elastomer sheet, it is extremely difficult to prevent positional deviation between electrodes to be inspected in the wafer and the conductive parts in the anisotropically conductive elastomer sheet upon the WLBI test even when the peripheral edge about the anisotropically conductive elastomer sheet is fixed by a frame plate having a coefficient of linear thermal expansion equivalent to that of the wafer.
As probe members for the WLBI test, are known those in which an anisotropically conductive elastomer sheet is fixed on a circuit board for inspection composed of, for example, a ceramic having a coefficient of linear thermal expansion equivalent to that of the wafer (see, for example, Japanese Patent Application Laid-Open Nos. 231019/1995 and 5666/1996, etc.). In such a probe member, as means for fixing the anisotropically conductive elastomer sheet to the circuit board for inspection, are considered a means of mechanically fixing peripheral portions about the anisotropically conductive elastomer sheet by, for example, screws or the like, a means of fixing it with an adhesive or the like, and the like.
However, in the means that the peripheral portions about the anisotropically conductive elastomer sheet are mechanically fixed by the screws or the like, it is extremely difficult to prevent positional deviation between electrodes to be inspected in the wafer and the conductive parts in the anisotropically conductive elastomer sheet for the same reasons of the means of being fixed by the frame plate as described above.
On the other hand, in the means of being fixed with the adhesive, it is necessary to apply the adhesive only to the insulating parts in the anisotropically conductive elastomer sheet in order to surely achieve electrical connection to the circuit board for inspection. However, since the anisotropically conductive elastomer sheet used in the WLBI test is small in the arrangement pitch of the conductive parts, and a clearance between adjacent conductive parts is small, it is extremely difficult in fact to do so. In the means of being fixed with the adhesive also, it is impossible to replace only the anisotropically conductive elastomer sheet by a new one when the anisotropically conductive elastomer sheet suffers from trouble, and so it is necessary to replace the whole probe member including the circuit board for inspection. As a result, increase in inspection cost is incurred.
In addition, as means for pressing the probe member against the object for inspection in the probe test or burn-in test, there have heretofore been used means by a load system that a load is applied to the probe member by a suitable pressing mechanism to pressurize the probe member. In order to electrically connect the probe member to the object for inspection stably and surely, it is necessary to apply a load of, for example, about 5 g per an electrode to be inspected.
When the object for inspection is a wafer having, for example, about 10,000 electrodes to be inspected, however, a load of at least 50 kg must be applied to the whole probe member. Therefore, a large-sized pressing mechanism is required, so that the inspection apparatus as a whole becomes considerably large.
Further, in the case a large-area wafer having a diameter of 8 inches or greater is inspected, scattering of loads applied to individual electrodes to be inspected occurs because difficulty is encountered on application of a load evenly to the whole wafer, so that it is difficult to achieve stable electrical connection to all the electrodes to be inspected.
In order to solve such problems, means utilizing a pressure reducing system have been proposed as means for pressing the probe member against the object for inspection (see Japanese Patent Application Laid-Open No. 5666/1996). The pressing means by this pressure reducing system are such that a water as an object for inspection is arranged in a box-type chamber opened at the top thereof, a probe member is arranged through an O-ring on the chamber so as to air-tightly close the opening of the chamber, and air within the chamber is evacuated to reduce the pressure in the interior of the chamber, thereby pressurizing the probe member by the atmospheric pressure.
According to the pressing means by such pressure reducing system, the inspection apparatus can be miniaturized because any large-sized pressing mechanism is not required, and moreover the whole wafer can be pressed by even force.
However, the pressing means by such pressure reducing system involves a problem that when air remains between an anisotropically conductive elastomer sheet in the probe member and a circuit board for inspection at the time the air within the chamber has been evacuated, both anisotropically conductive elastomer sheet and circuit board for inspection do not fully come into close contact with each other, so that stable electrical connection is not achieved.